This invention relates to a pump member using a novel ceramic material excellent in non-fusibility to a molten metal, and particularly to a pump member applicable to a hot-chamber type aluminium die casting machine.
In an aluminium die casting, a cold-chamber type die casting machine is generally used. Aluminium is molten in a vessel made of a heat-resistant metal or graphite. The molten aluminium is scooped with a ladle and poured into an injection sleeve coupled to a casting mold, followed by being compressed by a plunger to permit the molten aluminium to be introduced into the casting mold.
However, there are the following disadvantages.
The operation of manually pouring the molten aluminium from the vessel into the sleeve is very dangerous. This manual operation presents a bar in enhancing the productivity and operability of castings.
When the molten aluminium is poured into the injection sleeve, a temperature gradient of the molten aluminium is created between the section near to the inner wall surface of the sleeve and the central portion of the sleeve, since the sleeve is lower in temperature than the molten aluminium. In this way, the molten metal having such temperature gradient is introduced into the casting mold and then an aluminium casting is effected in a state different in the temperature of the molten metal, failing to obtain dense and uniform castings. Furthermore, cracks, waviness or blisters due to the penetration of gases are likely to be formed in the castings.
The conventional plunger and sleeve material should be normally preheated to 300.degree. to 350.degree. C and kept at this temperature, since it is impossible from the standpoint of their heat shock resistance and strength to rapidly heat them from room temperature up to the melting temperature of aluminium.
Furthermore, the compressing force of the molten metal is, of necessity, of the order of about 2 tons/cm.sup.2, since the molten metal has a temperature gradient during pouring into the sleeve and, during injection, is rapidly lowered in its temperature.
The conventional sleeve and plunger material are more or less under attack by the molten aluminium and, in an attempt to prevent their fusibility to the molten aluminium and attain a lengthy service life, the associated wall surfaces of the sleeve and plunger are coated with a coating material consisting of a mixture of graphite and oil. The coating material is found helpful in preventing the fusibility of these members to the molten aluminium. During compression, however, the oil is decomposed into carbons and hydrogens due to the heat of the molten aluminium. The hydrogen so formed is liable to be adsorbed in the aluminium, resulting in pin-holes and blisters being formed in castings.
As will be understood from the above, the cold-chamber type aluminium die casting machine has a variety of disadvantages. These disadvantages will be able to be almost all overcome if a hot-chamber type die casting machine as already realized in a low melting point metal die casting is realized in an aluminium die casting.
However, a hot-chamber type aluminium die casting has not been realized to date, since there is formed no material having a heat resisting strength, heat shock resistance and wear resistance sufficient to be usable at a temperature near to an aluminium casting temperature (the melting temperature of the aluminium is of the order of 660.degree.C) and not attacked by a molten aluminium.
The plunger and sleeve acting as a pipe for supplying a molten aluminium from the vessel into a casting mold are required to be both corrosion-resistant and non-fusible to the molten aluminium, even if the molten metal is directly poured, as well as be excellent in a heat shock resistance, high temperature strength and wear resistance.
With the hot-chamber type die casting machine it may safely be said that the plunger and sleeve functions as the heart of the machine. If there is any fault or damage of this section, the machine will not work as a whole.
To manufacture aluminium castings at a relatively low cost, it will be necessary from the commercial point of view to use a plunger and sleeve sufficient to be serviceable at more than 100,000 shots. From the above it will be understood that a variety of outstanding characteristics are required in realizing a hot-chamber type die casting machine.